1. Field of the Invention
The present invention relates to a medium storage device for recording data on a medium by a head and a medium rotation synchronization processing method, and more particularly to a medium storage device for decreasing the rotation jitter gap which is created anticipating the rotation jitter of a medium, and a medium rotation synchronization processing method.
2. Description of the Related Art
Because of the recent demands for the computerized processing of data, larger capacities are demanded for medium storage devices for storing the data, such as magnetic disk devices and optical disk devices. For this, the track density and recording density of a disk medium are increasing more and more. Also a decrease in unnecessary areas on tracks is demanded.
In the format of one track on the disk shown in FIG. 13, the data area 102 is created immediately after the servo area 100, and the servo area 100 is created for acquiring positioning information and for recognizing the start of the data areas. For example 10 pairs of the servo area 100 and the data area 102 continue on one track.
FIG. 13 shows the time axes of the rotation of the disk. If there is no rotation jitter and no eccentricity of the disk, then the space of the servo area 100 or the data area 102 becomes the same value “A”, as shown at the top in FIG. 13. If a rotation jitter and eccentricity of the disk exists, as shown at the bottom in FIG. 13, then the space of the servo area 100 or the data area 102 becomes “A1”, “A2” and “A3”, which are not constant values. Therefore when the read/write operation is controlled based on the time from the servo area 100, then all the data areas cannot be used since the data areas are not constant.
Therefore as FIG. 14 shows, a gap area 104 is created before and after the data area 102, and a preamble area 106 is created before the data area 102 to absorb this fluctuation. In other words, as the top in FIG. 14 shows, when the servo mark in the servo area 100 is detected (SSM found), a sector pulse of each data area 102 and read gate (same for write gate) are generated. By this, as the bottom in FIG. 14 shows, the read gate can cover at least the data area 102 even if a rotation jitter and eccentricity occur (e.g. Japanese Patent Application Laid-Open No. H11-031358).
This method is for generating a read gate by counting the clocks with a fixed frequency from the detection of the servo mark. Therefore as FIG. 14 shows, the servo gate and the read gate (same for write gate) do not completely match with the data area 102, and are shifted from the data area 102. For this, a specific length of the gap area 104 is required so that the shift causes no problems. This length is determined at designing anticipating the maximum eccentricity of the disk and the maximum rotation change value of the disk, which are expected.
Another prior method, as shown in FIG. 15, is proposed that calculates the frequency correction value by measuring this servo interval, and controls the start position (timing) of the read gate/write gate/servo gate, so that the synchronization relationship of the read gate and the data area is maintained even if an eccentricity of the disk and rotation fluctuation exist (e.g. Japanese Patent Application Laid-Open NO. 2002-133771). This method is called the DSW (Disk Synchronous Write) method.
Because of the recent demands for downsizing devices, such disk storage devices are also installed in compact servers and mobile equipment (e.g. notebook type personal computer and portable AV (Audio/Visual) equipment). Therefore such disk devices are used in environments which easily subject to the influence of the external environment, such as vibration and temperature change. This makes it possible to detect the servo synchronization mark in error.
So in the case of a conventional method for controlling (the changing clock frequency of) a read gate and write gate based on the measurement of the interval of servo synchronization marks, the DSW method cannot be used effectively if a servo synchronization mark is detected in error, where data corruption may occur.
Also the interval measurement error of servo synchronization marks may occur, so the DSW method cannot be used effectively, where data corruption may occur, and the data reliability of the disk storage device drops.